A silicon-on-sapphire (SOS) integrated circuit typically includes a plurality of spaced, isolated islands of single-crystalline silicon on the surface of a sapphire substrate. Each island may include a MOSFET which has source and drain regions spaced by a channel region, a channel oxide layer over at least the channel region and a conductive gate on the oxide layer and over the channel region. The various MOSFETs are electrically connected to form a desired circuit, such as a complementary MOS (CMOS) integrated circuit. The MOSFETs are typically electrically connected, at least in part, by conductive interconnects of doped polycrystalline silicon.
When SOS devices are subjected to radiation, the passage of radiation through the sapphire substrate creates secondary electrons. These secondary electrons have a high kinetic energy, greater than 20 electron volts for sapphire, which is rapidly lost through scattering events until they are thermalized to the conduction band. These electrons then drift in an electric field, causing current flow, until they are trapped, recombined with ionized core atoms, or pass through device contacts. Thus, in an SOS integrated circuit in which polycrystalline silicon conductive interconnects are directly on the surface of the sapphire substrate, the radiation generated electrons in the sapphire will flow directly into the interconnects which will conduct the electrons directly into field-effect transistors in the silicon islands. This flow of electrons can adversely affect the operation of the SOS integrated circuit.